1. Field of the Invention
The present invention relates to a cellular mobile communication system, and more particularly, to the improvement of coverage areas defined by mobile base stations.
2.Description of the Related Art
A prior art cellular mobile communication system includes a mobile control station and a plurality of mobile base stations. The mobile control station carries out call connection control for public switched telephone networks and call distribution control for the mobile base stations. In this case, a plurality of mobile tranceivers, i.e., antennas are provided at different sites, and each of the antennas is fixedly connected to one of the mobile base stations. That is, a service area defined by the mobile control station is divided into a plurality of coverage areas defined by the mobile stations, i.e., the antennas, which will be later explained in detail.
In the prior art system, however, since a coverage area defined by one of the mobile base stations is dependent upon a single antenna, large blind sections are present, to create a service interruption between the mobile stations and the mobile base station. Also, the distribution of power of waves within each of the coverage areas is not uniform, thus degrading the quality of communications between the mobile control station and the mobile stations.
Also, in the above-mentioned prior art system, the coverage area defined by one of the mobile base stations has been adjusted in consideration of expected distribution and density of mobile stations to service within the coverage area, as follows:
(1) A directional antenna or an omnidirectional antenna is adopted, and the horizontal directivity thereof is changed. Otherwise, downtilting of the antenna is adopted to change the vertical directivity thereof. In this case, however, since a mechanical adjustment is required, it is impossible to follow a rapid change of the distribution and density of mobile stations. PA1 (2) A power control system is adopted to change the power of waves generated from the antenna. In this case, however, when the power of the waves is too strong, an interruption is generated in waves used to service other adjacent coverage areas, while when the power of waves is too weak, unexpected blind sections are generated.
Thus, in the prior art system, since it is difficult to change the shape and size of each of the coverage areas, when the density of mobile stations being serviced becomes rapidly large in one coverage area, a congestion state may be locally generated therein.